This invention relates generally to automotive lighting systems and, in particular, to an automotive lamp with multiple reflectors and multiple light sources.
Generally, conventional automotive lighting systems utilize filament bulbs as a lighting source. However, filament bulbs have many drawbacks, including high consumption of electrical power, the generation of great amounts of heat, and readily breakable filaments. Recently, due to these drawbacks, light emitting semiconductor devices (LESDs), such as light emitting diodes (xe2x80x9cLEDsxe2x80x9d), have been adapted for use in certain automobile lighting systems.
LEDs solve many of the problems associated with filament bulbs, because they emit light using a lower voltage and current than used by a filament bulb and are less prone to breakage. However, various other problems are associated with LEDs when used in automobile lighting systems. For example, an individual LED is limited in its forward lighting power, because the low voltage associated with LEDs results in less lighting power than a filament lamp. Moreover, LEDs use a substantially planar luminescent element which radiates high intensity light predominantly in the forward direction, and only minimal light energy is emitted toward the sides. Thus, parabolic reflectors are typically not as useful in increasing the amount of light directed in the axis of the reflector.
Accordingly, an LED""s lighting power must be augmented when it is used in an automobile lighting system, such as a headlamp or a tail light. A headlamp requires that there be enough forward lighting power to illuminate the road and to meet the governmental restrictions placed on headlamps regarding the placement, brightness, and photometrics for such lamps. Further, LEDs used in tail lights are required to have enough lighting power to call attention to vehicles that the car ahead of them is stopping, in accordance with government regulations.
In order to augment the light emitted from a device comprising LEDs, it is generally necessary to combine a plurality of LED lamps into a single lighting device. The problem that has arisen with this solution is that of finding a way to combine a plurality of LEDs into a single lighting device of limited size, which is still capable of making a concentrated light beam that meets the specific intensity, beam spread, power consumption and size requirements of the industry. For example, the combination of two or more separate LED lamps within a single parabolic reflector as a means to increase the emitted light intensity results in projection of multiple separate beams with dark intermediate zones. This is not acceptable in a vehicle headlamp.
A second potential solution includes the use of multiple LEDs, each LED having its own reflector. This solution has not been acceptable in the past because the overall size limitation for the lighting device forces each individual reflector to be reduced in size, resulting in projected beams with unacceptably large individual divergences. Moreover, as the number of LEDs is increased, the amount of heat generated by the LEDs increases. Therefore, due to the size limitations on an automotive lighting system device, a need exists for an automotive lighting system that efficiently combines a plurality of LEDs into a single, compact lighting device while providing for dissipation or removal of excess heat generated by the lighting system.
One approach to solving the problem of light intensity is found in U.S. Pat. No. 5,782,553 to McDermott (xe2x80x9cthe ""553 patentxe2x80x9d). The ""553 patent discloses the use of a concave reflector to collect and concentrate light from a plurality of light sources. According to the ""553 patent, the light sources are embedded into various quadrants of a transparent medium such that emitted light passes through the medium and reflects off of a single concave reflector at the rear of the quadrants of the medium. The reflected light then passes back through the medium and finally exits the medium as a single beam of light. Accordingly, great care is needed in selecting an appropriate medium, as poor transmissivity of the medium will deleteriously affect the ultimate goal of increased light intensity. Notwithstanding the care taken in selecting the transparent medium, the ""553 patent contemplates significant transmission losses (up to 25%) in practicing the invention therein. It would be beneficial to obtain the benefit of multiple light sources without incurring the transmission losses as contemplated by the ""553 patent.
Another approach is disclosed in U.S. Pat. No. 6,412,971 B1 to Wojnarowski et al. (xe2x80x9cthe ""971 patentxe2x80x9d). The ""971 patent discloses a substrate upon which a number of LESDs are arranged. According to the ""971 patent, reflector components may be used in conjunction with the LESDs, much in the same way that reflector components are used with a filament bulb. Specifically, the reflector components extend upwardly and outwardly from the surface of the LESDs or the base of the LESDs if it is desired to reflect light emitted from the sides of the LESDs. In either application, however, the LESDs and their mountings are directly viewable. It would be advantageous, if the light source and its mounting were hidden from view so as to be more aesthetically pleasing.
It is desirable, therefore, to provide a multiple light source without incurring excessive transmission losses. Moreover, it is desired that the light assembly present an aesthetically pleasing form. It would be further advantageous if the light assembly could be formed into a variety of shapes and patterns. It would also be advantageous if the light assembly provided for dissipation of heat generated by the light source.
In accordance with the present invention, a light assembly is provided which overcomes the disadvantages of the prior art. According to the present invention, LESDs are mounted opposite to the reflective side of a reflector. A plurality of reflectors are arranged in an overlapping fashion such that the light emitted from the LESD of one reflector is directed to the reflective surface of an underlying reflector. In this fashion, a number of LESDs may be incorporated into a lighting device in a variety of patterns while maintaining the LESDs and their mountings hidden from view. Moreover, the reflectors may be used as cooling fins to dissipate heat generated from the LESDs or to direct the heat to a heat sink.
The invention provides a light assembly which may include a number of light sources without incurring excessive transmission losses. Moreover, the light assembly presents an aesthetically pleasing form since the light sources and their mountings are hidden from view. Additionally, the light assembly may be constructed in a variety of patterns. Moreover, the light assembly may easily be configured to dissipate heat generated from the LESDs or to direct the heat to a heat sink.